Oil burners employ a nozzle at the end of a fuel supply pipe to atomize liquid fuel oil and provide a diverging spray of small fuel oil droplets which can be readily ignited and burned. The atomized spray is ignited by a pair of electrodes having tips or points the ends of which are spaced apart to provide a spark gap. The electrodes are connected to a source of electrical power which produces an ignition spark when the gap is jumped by an electric current.
The width of the spark gap and the positioning of this gap relative to the atomized spray are critical. The width of the spark gap must be such that the electric current will jump the gap under the conditions at which the burner operates. For example, the gap width must provide a strong spark in the turbulent air currents caused by the fuel spray and each electrode must be positioned to prevent sparks from jumping to any other metal parts. The electrode tips also must remain out of the path of the spray droplets by a distance sufficient to prevent the formation of carbon deposits, but sufficiently close to the spray to ensure ignition of the fuel. If a failure of ignition results from an improper size or location of the gap, fuel may continue to enter the combustion chamber where an accumulated amount of liquid fuel may itself cause damage or be subsequently ignited with undesirable consequences, such as distribution of soot and/or fumes beyond the confines of the combustion chamber.
The adjustment of electrodes in conventional oil burners has been a tedious and exacting job in the past. The electrode tips must be positioned so as not to be wetted by the spray but close enough to it so that a spark across the gap will reliably ignite the spray and cause it to burn as a flame. The distance between the free ends of the electrode tips establishes the width of the spark gap, for example 1/8 inch, and this width must be set with a high degree of accuracy relative to the current and voltage available so as to provide the level of spark required. In addition, the position of the center of the gap must be set very precisely at a specific radial distance from the axis of the nozzle outlet and opposite a point on this axis that is located at a specific distance forward of the center of the nozzle outlet. In this specification, "setting" the spark gap means accomplishing all of these adjustments.